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  6.     <title>5.7.¬† Curves</title>
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  13.     <link rel="up" href="gimp-tools-color.html" title="5.¬† Color Tools" />
  14.     <link rel="prev" href="gimp-tool-levels.html" title="5.6.¬† Levels" />
  15.     <link rel="next" href="gimp-tool-posterize.html" title="5.8.¬†Posterize" />
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  18.     <div class="navheader">
  19.       <table width="100%" summary="Navigation header">
  20.         <tr>
  21.           <th colspan="3" align="center">5.7.¬†
  22.     <span lang="en" xml:lang="en">Curves</span>
  23.   </th>
  24.         </tr>
  25.         <tr>
  26.           <td width="20%" align="left"><a accesskey="p" href="gimp-tool-levels.html"><img src="../images/prev.png" alt="Prev" /></a>¬†</td>
  27.           <th width="60%" align="center">5.¬†
  28.     <span lang="en" xml:lang="en">Color Tools</span>
  29.   </th>
  30.           <td width="20%" align="right">¬†<a accesskey="n" href="gimp-tool-posterize.html"><img src="../images/next.png" alt="Next" /></a></td>
  31.         </tr>
  32.       </table>
  33.       <hr />
  34.     </div>
  35.     <div class="sect2" lang="en" xml:lang="en">
  36.       <div class="titlepage">
  37.         <div>
  38.           <div>
  39.             <h3 class="title"><a id="gimp-tool-curves"></a>5.7.¬†
  40.     <span lang="en" xml:lang="en">Curves</span>
  41.   </h3>
  42.           </div>
  43.           <div>
  44.             <div class="revhistory">
  45.               <table border="1" width="100%" summary="Revision history">
  46.                 <tr>
  47.                   <th align="left" valign="top" colspan="3">
  48.                     <b>Revision History</b>
  49.                   </th>
  50.                 </tr>
  51.                 <tr>
  52.                   <td align="left">Revision $Revision: 2429 $</td>
  53.                   <td align="left">2008-01-23</td>
  54.                   <td align="left">j.h</td>
  55.                 </tr>
  56.               </table>
  57.             </div>
  58.           </div>
  59.         </div>
  60.       </div>
  61.       <a id="id2646734" class="indexterm"></a>
  62.       <a id="id2646748" class="indexterm"></a>
  63.       <p>
  64.     The Curves tool is the most sophisticated tool for changing the color,
  65.     brightness, contrast or transparency of the active layer or a selection.
  66.     While the Levels tool allows you to work on Shadows and Highlights, the
  67.     Curves tool allows you to work on any tonal range. It works on RGB
  68.     images.
  69.   </p>
  70.       <div class="sect3" lang="en" xml:lang="en">
  71.         <div class="titlepage">
  72.           <div>
  73.             <div>
  74.               <h4 class="title"><a id="id2646767"></a>5.7.1.¬†
  75.       <span lang="en" xml:lang="en">Activate the Tool</span>
  76.     </h4>
  77.             </div>
  78.           </div>
  79.         </div>
  80.         <p>You can get to this tools in several ways :</p>
  81.         <div class="itemizedlist">
  82.           <ul type="disc">
  83.             <li>
  84.               <p>
  85.           In the image menu through
  86.           <span class="guimenu">Tools</span> ‚Üí <span class="guisubmenu">Color Tools</span> ‚Üí <span class="guimenuitem">Curves</span> or
  87.           <span class="guimenu">Colors</span> ‚Üí <span class="guimenuitem">Curves</span>.
  88.         </p>
  89.             </li>
  90.             <li>
  91.               <p>
  92.           By clicking on the tool icon
  93.           <span class="guiicon">
  94.             <span class="inlinemediaobject"><img src="../images/toolbox/stock-tool-curves-22.png" /></span>
  95.           </span>
  96.           in Toolbox, if this tool has been installed there (see
  97.           <a class="link" href="gimp-dialogs-misc.html#gimp-tools-dialog" title="5.1.¬† Tools Dialog">Tools dialog</a>.
  98.         </p>
  99.             </li>
  100.           </ul>
  101.         </div>
  102.       </div>
  103.       <div class="sect3" lang="en" xml:lang="en">
  104.         <div class="titlepage">
  105.           <div>
  106.             <div>
  107.               <h4 class="title"><a id="id2646875"></a>5.7.2.¬†
  108.       <span lang="en" xml:lang="en">
  109.         ‚Äú<span class="quote">Adjust Color Curves</span>‚Äù options
  110.       </span>
  111.     </h4>
  112.             </div>
  113.           </div>
  114.         </div>
  115.         <div class="figure">
  116.           <a id="id2646889"></a>
  117.           <p class="title">
  118.             <b>Figure¬†13.135.¬†
  119.         <span lang="en" xml:lang="en">
  120.           The ‚Äú<span class="quote">Adjust Color Curves</span>‚Äù dialog
  121.         </span>
  122.       </b>
  123.           </p>
  124.           <div class="figure-contents">
  125.             <div class="mediaobject">
  126.               <img src="../images/toolbox/tools-curves.png" alt="The Adjust Color Curves dialog" />
  127.             </div>
  128.           </div>
  129.         </div>
  130.         <br class="figure-break" />
  131.         <div class="variablelist">
  132.           <dl>
  133.             <dt>
  134.               <span class="term">Channel</span>
  135.             </dt>
  136.             <dd>
  137.               <p>
  138.             There are five options:
  139.           </p>
  140.               <div class="variablelist">
  141.                 <dl>
  142.                   <dt>
  143.                     <span class="term">
  144.                 <span lang="en" xml:lang="en">Value</span>
  145.               </span>
  146.                   </dt>
  147.                   <dd>
  148.                     <p>
  149.                   The curve represents the Value, i.e the brightness of
  150.                   pixels as you can see them in the composite image.
  151.                 </p>
  152.                   </dd>
  153.                   <dt>
  154.                     <span class="term">
  155.                 <span lang="en" xml:lang="en">Red; Green; Blue</span>
  156.               </span>
  157.                   </dt>
  158.                   <dd>
  159.                     <p>
  160.                   The curve represents the quantity of color in each of the
  161.                   three RGB channels. Here, <span class="emphasis"><em>dark</em></span> means
  162.                   <span class="emphasis"><em>little</em></span> of the color.
  163.                   <span class="emphasis"><em>Light</em></span> means <span class="emphasis"><em>a lot</em></span>
  164.                   of the color.
  165.                 </p>
  166.                   </dd>
  167.                   <dt>
  168.                     <span class="term">
  169.                 <span lang="en" xml:lang="en">Alpha</span>
  170.               </span>
  171.                   </dt>
  172.                   <dd>
  173.                     <p>
  174.                   The curve represents the opacity of the pixels.
  175.                   <span class="emphasis"><em>Dark</em></span> means
  176.                   <span class="emphasis"><em>very transparent</em></span>.
  177.                   <span class="emphasis"><em>Light</em></span> means <span class="emphasis"><em>very
  178.                   opaque</em></span>. Your image must have an Alpha channel
  179.                   for this option to be enabled.
  180.                 </p>
  181.                   </dd>
  182.                 </dl>
  183.               </div>
  184.             </dd>
  185.             <dt>
  186.               <span class="term">Reset Channel</span>
  187.             </dt>
  188.             <dd>
  189.               <p>
  190.             This button deletes all changes made to the selected channel and
  191.             returns to default values.
  192.           </p>
  193.             </dd>
  194.             <dt>
  195.               <span class="term">Linear and Logarithmic buttons</span>
  196.             </dt>
  197.             <dd>
  198.               <p>
  199.             These buttons allow to choose the Linear or Logarithmic type of
  200.             the histogram. You can also use the same options in Tool Options
  201.             dialog.
  202.           </p>
  203.             </dd>
  204.             <dt>
  205.               <span class="term">Main Editing Area</span>
  206.             </dt>
  207.             <dd>
  208.               <div class="itemizedlist">
  209.                 <ul type="disc">
  210.                   <li>
  211.                     <p>
  212.                 <span class="emphasis"><em>The vertical gradient</em></span>: it represents the
  213.                 the destination, the output tonal scale. It ranges from 0
  214.                 (black) to 255 (white), from Shadows to Highlights.
  215.               </p>
  216.                   </li>
  217.                   <li>
  218.                     <p>
  219.                 <span class="emphasis"><em>The horizontal gradient</em></span>: it represents
  220.                 the input tonal scale. It, too, ranges from 0 (black) to 255
  221.                 (white), from Shadows to Highlights. When you
  222.                 adjust the curve, it splits up into two parts; the upper part
  223.                 then represents the <span class="emphasis"><em>tonal balance</em></span> of the
  224.                 layer or selection.
  225.               </p>
  226.                   </li>
  227.                   <li>
  228.                     <p>
  229.                 <span class="emphasis"><em>The chart</em></span>: the curve is drawn on a grid
  230.                 and goes from the bottom left corner to the top right corner.
  231.                 The pointer x/y position is permanently displayed in the top
  232.                 left part of the grid. By default, this curve is straight,
  233.                 because every input level corresponds to the same
  234.                 ouput tone. GIMP automatically places an anchor at both
  235.                 ends of the curve, for black (0) and white (255).
  236.               </p>
  237.                     <p>
  238.                 If you click on the curve, a new <span class="emphasis"><em>anchor</em></span>
  239.                 is created. When the mouse pointer goes over an anchor, it
  240.                 takes the form of the moving crosshair. You can
  241.                 click-and-drag the anchor to bend the curve. If you click
  242.                 outside of the curve, an anchor is also created, and the
  243.                 curve includes it automatically.
  244.               </p>
  245.                     <p>
  246.                 Unactive anchors are black. The active anchor is white. You
  247.                 can activate an anchor by clicking on it. You can also swap
  248.                 the anchor activation by using the Left and Right arrow keys
  249.                 of your keyboard. You can move the anchor vertically with the
  250.                 Up and Down arrow keys. This allows you to fine tune the
  251.                 anchor position. Holding the <span class="keycap"><strong>Shift</strong></span> down lets
  252.                 you move it by increments of 15 pixels.
  253.               </p>
  254.                     <p>
  255.                 Two anchors define a <span class="emphasis"><em>curve segment</em></span> which
  256.                 represents a tonal range in the layer. You can click-and-drag
  257.                 this segment (this creates a new anchor). Of course, you
  258.                 can't drag it beyond the end anchors.
  259.               </p>
  260.                     <p>
  261.                 To delete all anchors (apart from both ends), click on the
  262.                 <span class="guilabel">Reset Channel</span> button. To delete only one
  263.                 anchor, move it onto another point or to the
  264.                 grid border.
  265.               </p>
  266.                     <p>
  267.                 Meanwhile, on the canvas, the mouse pointer has the form of
  268.                 an eye-dropper. If you click on a pixel, a vertical line
  269.                 appears on the chart, positioned to the source value of this
  270.                 pixel in the selected channel. If you Shift-click, you create
  271.                 an anchor in the selected channel. If you Ctrl-click, you
  272.                 create an anchor in all channels, possibly including the
  273.                 Alpha channel. You can also Shift-drag and Ctrl-drag: this
  274.                 will move the vertical line and the anchor will show up when
  275.                 releasing the mouse left button.
  276.               </p>
  277.                     <p>
  278.                 The histogram of the active layer or selection for the
  279.                 selected channel is represented grayed out in the chart. It's
  280.                 only a reference. 
  281.                 -->
  282.               </p>
  283.                   </li>
  284.                 </ul>
  285.               </div>
  286.             </dd>
  287.             <dt>
  288.               <span class="term">All Channels</span>
  289.             </dt>
  290.             <dd>
  291.               <p>
  292.             <span class="guilabel">Open</span>: This button allows you to select
  293.             a file holding curve settings.
  294.           </p>
  295.               <p>
  296.             <span class="guilabel">Save</span>: Allows you to save any curves
  297.             you have set to a file that can be loaded later.
  298.           </p>
  299.             </dd>
  300.             <dt>
  301.               <span class="term">Curve type</span>
  302.             </dt>
  303.             <dd>
  304.               <p>
  305.             <span class="guilabel">Smooth</span>: This mode constrains the curve
  306.             type to a smooth line with tension. It provides a more
  307.             realistic render than the following.
  308.           </p>
  309.               <p>
  310.             <span class="guilabel">Free</span>: With GIMP-v2.4, you are not totally
  311.             free to draw the curve. You actually draw a broken line that you
  312.             can smooth by clicking the <span class="guibutton">Smooth</span> button.
  313.           </p>
  314.             </dd>
  315.             <dt>
  316.               <span class="term">Preview</span>
  317.             </dt>
  318.             <dd>
  319.               <p>
  320.             The Preview button makes all changes to the levels dynamically so
  321.             that the new level settings can be viewed immediately.
  322.           </p>
  323.             </dd>
  324.           </dl>
  325.         </div>
  326.         <div class="variablelist">
  327.           <p class="title">
  328.             <b>
  329.         <span lang="en" xml:lang="en">Tool Options dialog</span>
  330.       </b>
  331.           </p>
  332.           <p>
  333.         Although this tool is not present in Tool box, nevertheless it has a
  334.         Tool Option Dialog under the Toolbox. These options are described
  335.         here:
  336.       </p>
  337.           <dl>
  338.             <dt>
  339.               <span class="term">Histogram Scale</span>
  340.             </dt>
  341.             <dd>
  342.               <p>
  343.             These two options have the same action as the logarithmic and
  344.             Linear buttons in the Curves dialog.
  345.           </p>
  346.             </dd>
  347.             <dt>
  348.               <span class="term">Sample Average</span>
  349.             </dt>
  350.             <dd>
  351.               <p>
  352.              This slider sets the ‚Äú<span class="quote">radius</span>‚Äù of the color-picking
  353.              area. This area appears as a more or less enlarged square
  354.              when you maintain the click on a pixel. Here, the eye-dropper is
  355.              used to locate a pixel: radius = 1 seems the best.
  356.           </p>
  357.             </dd>
  358.           </dl>
  359.         </div>
  360.       </div>
  361.       <div class="sect3" lang="en" xml:lang="en">
  362.         <div class="titlepage">
  363.           <div>
  364.             <div>
  365.               <h4 class="title"><a id="id2647426"></a>5.7.3.¬†
  366.       <span lang="en" xml:lang="en">Using the ‚Äú<span class="quote">Curves</span>‚Äù tool</span>
  367.     </h4>
  368.             </div>
  369.           </div>
  370.         </div>
  371.         <div class="variablelist">
  372.           <dl>
  373.             <dt>
  374.               <span class="term">Summary and basic shapes</span>
  375.             </dt>
  376.             <dd>
  377.               <p>
  378.             We create anchors and segments on the curve and we move them to
  379.             shape the curve. This curve maps ‚Äú<span class="quote">input</span>‚Äù tones of
  380.             the active layer or selection to ‚Äú<span class="quote">output</span>‚Äù tones.
  381.           </p>
  382.               <div class="figure">
  383.                 <a id="id2647472"></a>
  384.                 <p class="title">
  385.                   <b>Figure¬†13.136.¬†
  386.               <span lang="en" xml:lang="en">How the Curves tool works</span>
  387.             </b>
  388.                 </p>
  389.                 <div class="figure-contents">
  390.                   <div class="mediaobject">
  391.                     <img src="../images/toolbox/curves-work.png" alt="How the Curves tool works" />
  392.                     <div class="caption">
  393.                       <p>
  394.                   Moving the anchor of a pixel upwards makes this pixel
  395.                   brighter.
  396.                 </p>
  397.                     </div>
  398.                   </div>
  399.                 </div>
  400.               </div>
  401.               <br class="figure-break" />
  402.               <div class="figure">
  403.                 <a id="id2647510"></a>
  404.                 <p class="title">
  405.                   <b>Figure¬†13.137.¬†
  406.               <span lang="en" xml:lang="en">Making the curve more horizontal</span>
  407.             </b>
  408.                 </p>
  409.                 <div class="figure-contents">
  410.                   <div class="mediaobject">
  411.                     <img src="../images/toolbox/curves-horiz-1.png" alt="Making the curve more horizontal" />
  412.                     <div class="caption">
  413.                       <p>
  414.                   Making the curve more horizontal forces all the input tonal
  415.                   range to occupy a shrunk output tonal range.
  416.                 </p>
  417.                     </div>
  418.                   </div>
  419.                   <div class="mediaobject">
  420.                     <img src="../images/toolbox/curves-horiz-2.png" alt="Making the curve more horizontal" />
  421.                     <div class="caption">
  422.                       <p>
  423.                   The histogram shows the compression of pixels into the
  424.                   output range. Darkest and brightest pixels disappeared:
  425.                   contrast decreases.
  426.                 </p>
  427.                     </div>
  428.                   </div>
  429.                 </div>
  430.               </div>
  431.               <br class="figure-break" />
  432.               <div class="figure">
  433.                 <a id="id2647574"></a>
  434.                 <p class="title">
  435.                   <b>Figure¬†13.138.¬†
  436.               <span lang="en" xml:lang="en">Making the curve more vertical</span>
  437.             </b>
  438.                 </p>
  439.                 <div class="figure-contents">
  440.                   <div class="mediaobject">
  441.                     <img src="../images/toolbox/curves-vert-1.png" alt="Making the curve more vertical" />
  442.                     <div class="caption">
  443.                       <p>
  444.                   Moving the upper end point to the left and the lower end
  445.                   point to the right is the same as moving the white slider to
  446.                   the left and the black slider to the right in the Levels
  447.                   tool: all pixels whose value is more than the white point
  448.                   (the flat part of the curve) are made white (more colored /
  449.                   more opaque according to the selected channel). All pixels
  450.                   whose value is less than the black point (the lower
  451.                   flattened curve) are made black (black / completely
  452.                   transparent).
  453.                   Pixels corresponding to points of the curve that have moved
  454.                   up are made lighter. Pixels corresponding to points of the
  455.                   curve that have moved down are made darker  (green arrows).
  456.                   All these pixels will be extended to the whole output tonal
  457.                   range.
  458.                 </p>
  459.                     </div>
  460.                   </div>
  461.                   <div class="mediaobject">
  462.                     <img src="../images/toolbox/curves-vert-2.png" alt="Making the curve more vertical" />
  463.                     <div class="caption">
  464.                       <p>
  465.                   The histogram shows the extension of values, from black (0)
  466.                   to White (255): contrast is increased. Since the Value
  467.                   channel is selected, changes affect all color channels and
  468.                   colors increase.
  469.                 </p>
  470.                     </div>
  471.                   </div>
  472.                 </div>
  473.               </div>
  474.               <br class="figure-break" />
  475.             </dd>
  476.             <dt>
  477.               <span class="term">Practical cases</span>
  478.             </dt>
  479.             <dd>
  480.               <div class="figure">
  481.                 <a id="id2647665"></a>
  482.                 <p class="title">
  483.                   <b>Figure¬†13.139.¬†
  484.               <span lang="en" xml:lang="en">Invert colors</span>
  485.             </b>
  486.                 </p>
  487.                 <div class="figure-contents">
  488.                   <div class="mediaobject">
  489.                     <img src="../images/toolbox/curves-invert.png" alt="Invert colors" />
  490.                     <div class="caption">
  491.                       <p>
  492.                   Black is made White (fully colored / fully opaque). White
  493.                   is made black (black, fully transparent). All pixels adopt
  494.                   the complementary color. Why that? Because subtracting 255
  495.                   from the channel values gives the complementary color. For
  496.                   example: 19;197;248 a sky blue gives 255-19; 255-197;
  497.                   255-248 = 236;58;7, a bright red.
  498.                 </p>
  499.                     </div>
  500.                   </div>
  501.                 </div>
  502.               </div>
  503.               <br class="figure-break" />
  504.               <div class="figure">
  505.                 <a id="id2647708"></a>
  506.                 <p class="title">
  507.                   <b>Figure¬†13.140.¬†
  508.               <span lang="en" xml:lang="en">Enhance contrast</span>
  509.             </b>
  510.                 </p>
  511.                 <div class="figure-contents">
  512.                   <div class="mediaobject">
  513.                     <img src="../images/toolbox/curves-H-S.png" alt="Enhance contrast" />
  514.                     <div class="caption">
  515.                       <p>
  516.                   Contrast is increased in mid tones because the curve is
  517.                   steeper there. Highlights and Shadows are increased but
  518.                   contrast is slightly less in these areas because the curve
  519.                   is flatter.
  520.                 </p>
  521.                     </div>
  522.                   </div>
  523.                 </div>
  524.               </div>
  525.               <br class="figure-break" />
  526.               <div class="figure">
  527.                 <a id="id2647748"></a>
  528.                 <p class="title">
  529.                   <b>Figure¬†13.141.¬†
  530.               <span lang="en" xml:lang="en">Working on color channels</span>
  531.             </b>
  532.                 </p>
  533.                 <div class="figure-contents">
  534.                   <div class="mediaobject">
  535.                     <img src="../images/toolbox/curves-lighten-1.png" alt="Working on color channels" />
  536.                     <div class="caption">
  537.                       <p>
  538.                   For every channel, we moved the white point horizontally to
  539.                   the left, to the first Highlights. This lightens Highlights
  540.                   up. Then we shaped the curve to lighten Mid tons and
  541.                   Shadows while keeping black.
  542.                 </p>
  543.                     </div>
  544.                   </div>
  545.                 </div>
  546.               </div>
  547.               <br class="figure-break" />
  548.               <div class="mediaobject">
  549.                 <img src="../images/toolbox/curves-lighten-2.png" />
  550.                 <div class="caption">
  551.                   <p>The original image and the result.</p>
  552.                 </div>
  553.               </div>
  554.             </dd>
  555.           </dl>
  556.         </div>
  557.       </div>
  558.     </div>
  559.     <div class="navfooter">
  560.       <hr />
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  562.         <tr>
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  564.           <td width="20%" align="center">
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  572.           <td width="40%" align="left" valign="top"><a accesskey="p" href="gimp-tool-levels.html">5.6.¬†
  573.     <span lang="en" xml:lang="en">Levels</span>
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  586.